Liquid fuel injection system

A liquid fuel injection system includes an injection unit (15) for atomizing liquid through application to the fuel vibration energy induced by the operation of piezoelectric/electrostriction elements, and a discharge valve (14) for discharging pressurized fuel into the injection unit (15). Only during a period of time when an intake valve (22) of an internal combustion engine is closed, an electric controller (30) supplies a drive voltage signal of a certain frequency to the piezoelectric/electrostriction elements of the injection unit so as to operate the piezoelectric/electrostriction elements, and a valve-opening drive signal to the discharge valve so as to discharge fuel into the injection unit from a fuel path of the discharge valve.